Soundproofing a Wall over an Existing Wall Part 2 Soundproofing a Wall over an Existing Wall Part 2
This is Part 2 of a 2 part series. To return to Part 1, click here.)
While the methods used in soundproofing a wall are very similar to constructing a new wall, they are sometimes more effective because the additional layers of drywall supply extra soundproofing and mass, which dampens low frequency sound. A wall’s soundproofing characteristics are measured by STC (Sound Transmission Class). Normal general conversation can be picked up and understood through a wall with an STC 25 rating. When this rating is increased to STC 60, not a difficult accomplishment, raised voices can still be heard but won’t be understood. The inside walls of most homes are not packed with insulation. With only one layer of drywall attached to the supporting studs, the STC rating approaches 34. Loud voices can be heard and understood on the other side of the wall. If the house is an old one and has settled, openings and gaps will make the situation worse.
Step 1: Estimating the Insulation
Working with insulation is relatively easy. Strength or great skill is not required. The batts or rolls of insulation should fit neatly between the supporting furring. Any trimming required will be around doors, plumbing, windows and electrical outlets. The insulation is easily cut with a trimming knife and the material is fairly lightweight. A measurement from ceiling to floor should be taken to find out how much insulating material to buy. This should be multiplied by the number of spaces that need to be filled between the studs to give you your total requirements. The gap between the studs should be measured, which will indicate what width of material to buy. To work out how many rolls you will need, divide the total required by the length of a roll, usually 8 feet (the standard floor to ceiling height).
Step 2: Inserting the Insulation
A standard roll of insulation is usually 8 feet and won’t require trimming after being inserted between the studs. Press the material in between the studs and trim around all electrical points. If you have bought a roll, the insulation may be stretched out on the floor or pushed into the cavity space and unrolled to the bottom where it can be trimmed with the trimming knife. If the insulation is a neat fit it will remain in place without fixing it to the studs. However some insulation is manufactured with a paper backing slightly wider than the roll and this may be stapled to the studs. The normal insulation requires a neat fit to hold it in place.
Step 3: Finishing
Once the insulation is in place, the first soundproof board can be nailed to the studs. The second board can now be fixed over the first making sure to stagger the joints. Tape may be applied to the joins and any gaps filled with caulking. The wall may now be painted.
It is important never to compress the soundproofing material. This may seem trivial but the materials effectiveness is reduced by displacing the air in the fibers. If the roll is too long never fold it over to make it fit. Trim it to the correct size. Clean your work clothes separately from your other clothes and rinse twice.